1. Field of the Invention
The present invention relates to a method for measuring a receiving-end bit error rate of a transmission link (cable, satellite or terrestrial) of a DVB (digital video broadcasting) transmission system.
2. Description of the Background Art
In the DVB transmission system via cable (DVB-C), satellite (DVB-S), or via terrestrial transmitters (DVB-T) now introduced as a result of standardization, a data stream to be transmitted is fed, in accordance with FIG. 1, in a standardized MPEG2 data format to a channel encoder 2 having a Reed-Solomon encoder 3 in a transmitter 1. After passing through a filter and I/Q modulator 4, the I- and Q-components generated in the channel encoder 2 are converted from the intermediate frequency IF into the highfrequency RF range and then transmitted via cable, satellite or terrestrial transmitters as a transmission link to a receiver 10, in which, in the reverse order, the data are decoded again by a Reed-Solomon decoder 12 after conversion to the intermediate frequency IF and also filtering and I/Q demodulation in the demodulator 11. The data MPEG2 stream retrieved in this way is then decoded in an MPEG2 decoder 13 and processed further as a video and audio signal.
The DVB transmission system with its various components is known and is described in greater detail in the DVB standard ETS 300429, ETS 300421, and ETS 300744 or in Digitale Fernsehtechnik (Digital television engineering) by Reimers U. published by Springer 1997.
The Reed-Solomon encoders and decoders used in this connection are also known and are described in Digitale Fernsehtechnik (Digital television engineering) by Reimers U. published by Springer 1997, and in Error Control Coding by Lin S. and Costello D. J. published by Prentice-Hall 1983.
An important criterion for the transmission quality of such a DVB transmission system is the bit error rate. To measure the bit error rate at the receiving end, it is known to switch off the entire encoding system and, with the Reeds Solomon encoder and decoder switched off, to measure the bit error rate by injecting a test signal (EP-A-0 752 769, page 2, lines 17-22). It is furthermore known to calculate the bit error rate from the number of corrected symbols in the Reed-Solomon decoder (EP-0 752 769). The first method is very time-consuming and requires an appreciable intervention in the entire transmission system, while the second method involving the indirect determination of the bit error rate is not accurate enough.